The present invention relates to rotary drum filtering apparatus and more particularly to the drum structure of rotary drum filtering apparatus such as, for example, rotary drum filters, thickeners, washers and the like of the type employed for filtering a slurry such as pulp stock.
Conventionally, rotary drum filtering apparatus of this general type have included a drum structure that supports a circumferential filter medium and contains filtrate compartments communicating with the openings in the filter medium for receiving liquid drained through the latter.
A rotary drum filtering apparatus, such as a rotary drum washer 10, is illustrated in FIG. 1. The traditional vacuum drum washer 10 includes a tank 14 having a baffled net box 18 and an net lip 22. Pulp entering the drum washer 10 passes over the lip 22 into an area 26 around a central drum 30. The central drum 30 is comprised of a plurality of fly rings 34 held together spaced apart, the outer circumference of the drum supporting washer decking 38. Pulp accumulates on the decking 38 and then is removed from the decking by a takeoff 42. The takeoff 42 deposits the pulp into an area 46 where a repulper 50 transports the pulp for further processing.
The fly ring is an integral part of the rotary washer drum's structure. It is located on the inside of the drum and its purpose is to maintain the round cross-section required to resist the loading seen by the drum while in operation.
The manufacturing process to make a fly ring 34 has been stagnating for decades. The traditional rotary drum washer fly ring manufacturing methods involve laser cutting, welding, machining, and straightening. Although laser cutting is used, the laser cutting, together with further processing, has not produced fly ring with an outer circumference within needed tight tolerances.
This prior fly ring construction illustrated in FIGS. 2 and 3 consisted of 5 laser cut segments that were assembled by grinding a weld preparation on each end of each ring segment, welding the ring segment ends together, grinding the weld, and then straightening the ring. The fly ring would then be machined to the proper finished outside diameter. This process is extremely labor intensive.
More particularly, the manufacturing of this ring involves the following steps: 1. Cut sections of the ring out of raw plate. 2. Produce weld preparations of both sides of the ring sections. 3. Position/Fixture the plates. 4. Weld each joint on one side. 5. Grind weld flat. 6. Flip over ring. 7. Weld each joint on opposite side. 8. Grind weld flat. 9. Straighten ring. 10. Machine outside diameter to finished dimension.